The present invention relates to a grease composition, in particular a grease composition that is used as a lubricant for gears and sliding parts. The present invention specifically relates to a grease composition that is excellent in lubricity even at low temperatures, abrasion resistance, and anti-seizure property, and is suitable for use with electrical equipment of marine engines, air craft engines, and vehicle engines, which require grease providing long service life, for example, starters including various sliding parts and gears such as helical gears, reduction gears, drive shafts, and levers.
A starter for starting up marine engines, aircraft engines, and vehicle engines usually has a pinion gear, which is driven via an overrunning clutch by a drive shaft of a motor. Upon switching on the motor for start-up, a magnet coil is excited to cause a lever to slide the pinion gear toward a ring gear provided on the output shaft of an engine. The pinion gear then meshes with the ring gear to rotate and start up the engine.
An engine starter has various sliding parts and gears. For lubrication of such parts, greases are mainly used which contain a base grease composed of a lubricating base oil and a thickener such as a lithium soap, and additives such as molybdenum disulfide or molybdenum dithiocarbamate.
Greases for various engine starters are required to have properties to enable smooth start-up even at low temperatures (lubricity at low temperatures), abrasion resistance, anti-seizure property, heat resistance, and low friction. However, properties of conventional greases cannot keep up with the recent increase in frequency of engine starter activation due to the recent effort to stop idling of vehicle engines for reducing emission in the light of global environmental problems. Thus there is a strong demand for improvement in particularly abrasion resistance and anti-seizure property of greases in order to prolong their service life.
In addition, greases for engine starters are demanded that will not adversely affect the electric contacts of the engine starters.
It is therefore an object of the present invention to provide a grease composition that has excellent abrasion resistance and anti-seizure property, long service life, exhibits excellent lubricity even at low temperatures, and has no adverse effect on electric contacts.
It is another object of the present invention to provide a grease composition suitable for use with electrical equipment and engine starters of vehicles and the like, which has excellent abrasion resistance and anti-seizure property, long service life, exhibits excellent lubricity even at low temperatures, and has no adverse effect on electric contacts, as well as a method for lubricating a vehicle electrical equipment or an engine starter with this composition.
According to the present invention, there is provided a grease composition comprising:
(A) a silicon-free synthetic oil having a kinematic viscosity of 10 to 60 mm2/s at 40xc2x0 C.;
(B) a urea thickener;
(C) melamine cyanurate; and
(D) polytetrafluoroethylene.
According to the present invention, there is also provided a lubricating method comprising applying the above grease composition to a vehicle electrical equipment or an engine starter having an electric contact, or use of the grease composition.
The present invention will now be explained in detail.
Component (A) of the present grease composition is a synthetic oil that contains no silicon and has a specific kinematic viscosity. Examples of such a silicon-free synthetic oil may include poly-xcex1-olefins such as polybutene, 1-octene oligomer, and 1-decene oligomer, and hydrides thereof; diesters such as ditridecyl glutarate, di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate, and di-3-ethylhexyl sebacate; polyol esters such as trimethylolpropane caprylate, trimethylolpropane pelargonate, pentaerythritol-2-ethylhexanoate, and pentaerythritol pelargonate; alkylnaphthalene; alkylbenzene; polyoxyalkylene glycol; polyphenyl ether; dialkyl diphenyl ether; and mixtures thereof. Among these examples, poly-xcex1-olefins, diesters, polyol esters, and mixtures thereof are preferably used.
Synthetic oils containing silicon, such as silicon oil, which have adverse effect on electric contacts, cannot be used.
The kinematic viscosity of component (A) at 40xc2x0 C. should be not lower than 10 mm2/s, preferably not lower than 15 mm2/s, for suppressing evaporation at elevated temperatures and for preventing solidification of the grease to achieve sufficiently long lubricating life, and should be not higher than 60 mm2/s, preferably not higher than 50 mm2/s, for achieving sufficient lubricity at low temperatures.
As component (A), a mixture of a plurality of synthetic oils may be used, as long as the kinematic viscosity of the mixture falls within the above-mentioned range. It is not mandatory that each and every synthetic oil in the mixture has a kinematic viscosity within the range mentioned above. It is yet preferred, for giving the grease sufficient fluidity at low temperatures, that each and every synthetic oil in the mixture has a kinematic viscosity that falls within the above-mentioned range.
According to the present invention, the amount of component (A) contained in the grease composition is not particularly limited. However, in order to eliminate any possibility that the grease becomes too solid to exhibit sufficient lubricity, the content of component (A) is preferably not less than 50% by weight, more preferably not less than 60% by weight of the grease composition, and preferably not more than 95% by weight, more preferably not more than 90% by weight of the grease composition.
Component (A) constitute a base oil in the grease composition of the present invention. In addition to the synthetic oil of component (A), the base oil of the present grease composition may also contain a mineral oil, such as paraffin or naphthene oil, as long as the desired advantages of the present invention are achieved.
A mineral oil may have anadverse effect on electric contacts, and may impair the fluidity of the grease at low temperatures. Thus, the content of the mineral oil is preferably not more than 20% by weight, more preferably not more than 10% by weight of the grease composition, and most preferably, no mineral oil is contained in the grease composition.
The kinematic viscosity of the mineral oil is not particularly limited. However, for suppressing evaporation at higher temperatures and for preventing solidification of the grease to achieve sufficiently long lubricating life, the kinematic viscosity of the mineral oil at 40xc2x0 C. is preferably not lower than 10 mm2/s, more preferably not lower than 15 mm2/s. On the other hand, for giving sufficient lubricity at low temperatures, the kinematic viscosity of the mineral oil is preferably not higher than 100 mm2/s, more preferably not higher than 80 mm2/s.
Component (B) of the present grease composition is a urea thickener. The urea thickener may be selected from, for example, urea compounds, urea-urethane compounds, urethane compounds, and mixtures thereof.
Examples of the urea compounds, urea-urethane compounds, and urethane compounds may include diurea compounds, triurea compounds, tetraurea compounds, polyurea compounds (other than di-, tri-, and tetraurea compounds), urea-urethane compounds, diurethane compounds, and mixtures thereof. Among these, diurea compounds, urea-urethane compounds, diurethane compounds, and mixtures thereof are particularly preferred.
More specifically, the urea thickener may preferably be a compound, or a mixture of compounds represented by the formula (1):
Xxe2x80x94CONHxe2x80x94R1xe2x80x94NHCOxe2x80x94Y xe2x80x83xe2x80x83(1) 
In the formula (1), R1 stands for a divalent hydrocarbon group, and X and Y may be the same or different groups, each standing for xe2x80x94NHR2, xe2x80x94NR3R4, or xe2x80x94OR5, wherein R2, R3, R4, and R5 may be the same or different groups, each standing for a hydrocarbon group having 6 to 20 carbon atoms.
R1 in the formula (1) is a divalent hydrocarbon group having preferably 6 to 20, more preferably 6 to 15 carbon atoms. Examples of the divalent hydrocarbon group may include a straight or branched alkylene group, a straight or branched alkenylene group, a cycloalkylene group, and an aromatic group. R1 may specifically be an ethylene group, a 2,2-dimethyl-4-methylhexylene group, or one of the groups represented by the following formulae: 
Among these, the following groups are particularly preferred: 
Each of R2, R3, R4, and R5 may be, for example, a straight or branched alkyl group, a straight or branched alkenyl group, a cycloalkyl group, an alkylcycloalkyl group, an aryl group, an alkylaryl group, or an arylalkyl group. More specific examples of these groups may include a straight or branched alkyl group such as a hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl, or icosyl group; a straight or branched alkenyl group such as a hexenyl, heptenyl, octenyl, nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl, pentadecenyl, hexadecenyl, heptadecenyl, octadecenyl, nonadecenyl, or eicosenyl group; a cyclohexyl group; an alkylcycloalkyl group such as a methylcyclohexyl, dimethylcyclohexyl, ethylcyclohexyl, diethylcyclohexyl, propylcyclohexyl, isopropylcyclohexyl, 1-methyl-3-propylcyclohexyl, butylcyclohexyl, amylcyclohexyl, amylmethylcyclohexyl, hexylcyclohexyl, heptylcyclohexyl, octylcyclohexyl, nonylcyclohexyl, decylcyclohexyl, undecylcyclohexyl, dodecylcyclohexyl, tridecylcyclohexyl, or tetradecylcyclohexyl group; an aryl group such as a phenyl or naphthyl group; an alkylaryl group such as a toluyl, ethylphenyl, xylyl, propylphenyl, cumenyl, methylnaphthyl, ethylnaphthyl, dimethylnaphthyl, or propylnaphthyl group; or an arylalkyl group such as a benzyl, methylbenzyl, or ethylbenzyl group. Among these, cyclohexyl, octadecyl, and toluyl groups are particularly preferred.
A diurea, urea-urethane, or diurethane compound as component (B) may be prepared by reacting a diisocyanate represented by the formula OCNxe2x80x94R1xe2x80x94NCO with a compound represented by the formula R2NH2, R3R4NH, or R5OH, or a mixture thereof, in the base oil at 10 to 200xc2x0 C., wherein R1, R2, R3, R4, and R5 are the same as those in the formula (1).
According to the present invention, the amount of component (B) in the grease composition is not particularly limited. However, for exhibiting its effect as a thickener, component (B) is contained in an amount of preferably not less than 2% by weight, more preferably not less than 5% by weight of the grease composition. On the other hand, in order not to impair the lubricity of the grease, the content of component (B) is preferably not more than 30% by weight, more preferably not more than 20% by weight of the grease composition.
Component (C) of the present invention is melamine cyanurate. Component (C) is a product of an addition reaction between 1 mole of melamine and 1 mole of cyanuric acid or isocyanuric acid, and is in the form of white powders having cleavage like molybdenum disulfide and graphite, wherein melamine molecules with a six-membered ring structure are firmly bonded with cyanuric acid or isocyanuric acid molecules via hydrogen bonds in a plane to form a layer, and a plurality of such layers are weakly bonded with each other. The primary particle size of the white powders is usually 0.5 to 5 xcexcm.
Component (C) may be prepared by any method. For example, component (C) may readily be obtained as a white precipitate by mixing an aqueous solution of melamine and an aqueous solution of cyanuric acid or isocyanuric acid. Component (C) may alternatively be prepared by reacting an aqueous dispersion of melamine and one or both of cyanuric acid and isocyanuric acid dispersed as the solid phase.
The content of component (C) is not particularly limited, and is preferably 0.1 to 20% by weight, more preferably 0.5 to 10% by weight of the grease composition.
Component (D) of the present grease composition is polytetrafluoroethylene.
Component (D) is in the form of white powders having a structure represented by the formula xe2x80x94(CF2xe2x80x94CF2)nxe2x80x94, wherein carbon atoms and fluorine atoms are bonded by strong binding energy.
Component (D) may be powders known as molding powders that may be molded into various molded products, pipes, and sheets, or fine powders that may be obtained by suspension polymerization or emulsion polymerization, and has excellent heat resistance, chemical inertness, and low friction.
The amount of component (D) in the grease composition is not particularly limited, and may preferably be 0.1 to 20% by weight, more preferably 0.5 to 10% by weight of the grease composition.
The grease composition of the present invention may also contain, as desired for further improving its performance, a solid lubricant, an extreme pressure agent, an anti-oxidant, a metal deactivator, an oilness agent, a rust-inhibitor, a viscosity index improver, or mixtures thereof, as long as the properties of the composition are not impaired.
The solid lubricant may be selected from, for example, graphite, fluorinated carbon black, borates of alkali metals, borates of alkaline earth metals, magnesium oxide, or zinc oxide.
The extreme pressure agent may be selected from, for example, phosphates or phosphites.
The anti-oxidant may be selected from, for example, phenol compounds such as 2,6-di-t-butylphenol or 2,6-di-t-butyl-p-cresol; amine compounds such as dialkyldiphenylamine, phenyl-xcex1-naphthylamine, or palkylphenyl-xcex1-naphthylamine; or phenothiazine compounds.
The metal deactivator may be selected from, for example, benzotriazole, benzothiazole, or sodium nitrite.
The oilness agent maybe selected from, for example, amines such as laurylamine, myristylamine, palmitylamine, stearylamine, or oleylamine; higher alcohols such as lauryl alcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol, or oleyl alcohol; higher fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid, or oleic acid; fatty acid esters such as methyl laurate, methyl myristate, methyl palmitate, methyl stearate, or methyl oleate; or amides such as laurylamide, myristylamide, palmitylamide, stearylamide, or oleylamide.
The rust-inhibitor may be selected from, for example, neutral or overbased petroleum or synthetic oil metal sulfonates such as neutral or overbased calcium sulfonates, neutral or overbased barium sulfonates, neutral or overbased zinc sulfonates; metal soaps; partially esterified polyhydric alcohols such as sorbitan fatty acid esters; amines; phosphoric acid; or phosphates.
The viscosity index improver may be selected from, for example, polymethacrylate, polyisobutylene, or polystylene.
It is of course not preferred to use any additives that may adversely affect the electric contacts.
Examples of such additives that may adversely affect the electric contacts may include molybdenum disulfide; metal dithiocarbamates such as molybdenum dithiocarbamate or zinc dithiocarbamate; metal dithiophosphates such as molybdenum dithiophosphate or zinc dithiophosphate; polysulfides; sulfur extreme pressure agents such as sulfurized oils and fats; or silicone defoaming agents.
There is no particular limitation imposed on the process for preparing the grease composition according to the present invention. For example, the grease composition may be prepared by adding, to the base lubricating oil of component (A), components (B), (C), and (D), and other additives if desired, stirring, and passing the resulting mixture through a roll mill or the like. Alternatively, the grease composition may also be prepared by adding and dissolving the starting material components for the thickener of component (B) in the base lubricating oil of component (A), stirring the resulting mixture to prepare component (B) in component (A), adding components (C) and (D) as well as other additives if desired, stirring, and passing the resulting mixture through a roll mill or the like.
The grease composition of the present invention is used as a lubricant for gears and sliding parts, and is particularly preferred for use with electrical equipment of marine engines, air craft engines, and vehicle engines, such as starters including various sliding parts and gears such as helical gears, reduction gears, drive shafts, and levers.
The grease composition of the present invention contains (A) a silicon-free synthetic oil having a specific kinematic viscosity, (B) a urea thickener, (C) melamine cyanurate, and (D) polytetrafluoroethylene, so that the composition has excellent abrasion resistance and anti-seizure property, long service life, and excellent lubricity even at low temperatures, and has no adverse effect on electric contacts. The present grease composition is thus particularly suitable for use with vehicle electrical equipment and vehicle engine starters.